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It's always hard to make an exhaust system which pleases everyone. Some like them loud, some not so. Even in our own case as enthusiasts we understand that there is no perfect exhaust system when it comes to sound level and noise.

Exhaust note and sound level is something that is always a compromise on a fixed system. Sometimes you feel you it’s not loud enough and other times too loud depending on what you have purchased.

To have both in one package is the ultimate solution so you can choose.

Creating a well engineered product is not so simple especially when you have so many variables such as back pressure, power output, sound volume and sound type in the equation.

We have seen numerous times where the current systems lose power on the quiet setting with an acceptable sound level and then do not lose power on the louder setting but are simply too loud.

We have gone as far as possible in our development and testing process for both power outputs, sound type and sound level.

Our Objectives:

Sound:

- Noise level and type to be sporty, smooth and sophisticated with the valve closed

- Minimal or zero drone with valve closed

- Valve open noise to be epic without being too loud and something you can actually enjoy without being embarrassed.

- Valve open noise to have a great pitch

- The difference between the valves open and closed not to just be a difference in sound level but also sound type (very adventures from a design point)

Engine Power Output:

- Power output not to change with the valve open or closed (This is not easy!)

- Dyno Testing as part of the development process

- Back Pressure testing as part of the development process

Installation / Servicing:

- Easy of installation of the physical exhaust

- Easy installation of the electronics which control the valve position

- Valve operation to be electronic with a keyfob

- Valve assembly to be easily removed in case of failure (will come with a lifetime warranty)

- A good range of high quality tail pipes

- Tail pipes to be individual and adjustable so individual stagger or length can be setup depending on individual taste and/or rear diffuser type

The Development:

The most difficult aspect of the development was to keep the power output of the S65 engine the same with the valves open or closed. For the evolve team it was unacceptable to lose any power when the valve is closed. It is very easy to make a valve based system where the back pressure dramatically increases with the valve closed. The most common method of creating a valve system is to put the valve on the end of one of the tail pipes on a regular fixed exhaust system.

When this is done the cross sectional area of the perforated section reduces and creates a huge amount of back pressure. This is wrong.

The Evolve E-Tronic uses two completely different paths when the valve is open or closed. We calculate and test different lengths and cross sectional areas of perforated tubes which take different paths.

So how do we start the process?

The first step is to fit pressure sensors across the entire stock BMW system. We fitted pressure sensors after the primary CAT, after the secondary CAT and just before the rear exhaust.

We take a measurement at different RPM’s and then during a dyno test.

A completely free flow system is then fitted without CAT’s and a straight through rear silencer. Pressure testing is done again.

Of course, we all know the results on the dyno of such a change and it’s around +20-30hp / 30lb.ft torque.

The aim is then to achieve the same power output but with a system with secondary CAT’s, mid silencers and a rear exhaust with two different paths for the exhaust gasses to exit (valve).

Alot of time is taken at this stage to achieve the goal.

Once this is achieved then comes a part which is in some ways even more difficult and time consuming – the noise type and pitch with both the valves open and closed while maintaining a zero power loss of the fully optimised system. The worst part is where we to make the valve rear silencer sound great with and without a primary DECAT and X Pipe!

Before we even started this process we spoke to many people and what they think is the best noise level and what they want the exhaust to sound like.

We already had alot of previous experience with the evolve X Pipe and fixed rear exhaust which sounded totally unique. Maybe a little too unique for the wider audience.

The results clearly show there is no real measureable difference in engine power output with the valves open or closed.
The pressure tests show a small increase in back pressure but this is not enough to make any real difference in engine power output. An approximate average increase of 0.10 Bar is seen through the exhaust system.

2) Evolve E-Tronic Rear Exhaust + Factory X Pipe

The results clearly show there is no real measureable difference in engine power output with the valves open or closed.
The pressure tests show a small different in back pressure but this is not enough to make any real difference in engine power output. An approximate average increase of 0.15 Bar is seen through the exhaust system.

Additionally, you can also see an average difference in pressure drop of approximate average of 0.5 Bar before the secondary CAT’s by deleting the primary CAT’s. This is why the power increase is so vast from a primary decat. Not just because of such a larger pressure drop but one that is so close to the engine.

The main result is that we do not lose power with our valve exhaust on the quiet setting. To lose power the back pressure increase towards the rear end of the car needs to be very large.

3) The dyno results show that our full system performs to the same level as any other X-Pipe/CAT/Rear Exhaust Setups with both valves open or closed.

Images of pressure sensors locations:

sAdditional information for readers to analyse results

As you can see from the dyno data every run has information about ignition timing and lambda.
We have shown what the stock ignition and lambda targets from the factory software below so you can have a better understanding of what’s going on.
Please note these are ‘targets’ and the actual end result has the effects of many variables.

We hope the above information serves to be useful to the readers and shows the extent we go to when developing a product.